I didn't really see anything wrong with this; it was an interesting start. I think the most glaring things were your use of "fleed" instead of "fled," and in the sentence "One of the dark figures grabbed her and launched themself back to the top of the stadium," themself is grammatically incorrect because of "one." Other than that, though, a pretty good start )

This is a good start for a first chapter but I think you gave too much away. The writing was good, it seems to fit for the type of story that you're going for. But everything went way too fast in only a few words. That set the flow off. You should spend more time describing the scene and the characters and lengthen it a bit. Other than that, nice try.